The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
Free tracker included with every download this week
Mounjaro and Gas: What You Need to Know
Farting and digestive discomfort are common side effects reported by people taking Mounjaro (tirzepatide) in the UK. This happens because Mounjaro slows how quickly food moves through your stomach and changes how your gut processes food. While uncomfortable, these symptoms are typically temporary and often improve as your body adjusts to the medication. Understanding what causes these changes and how to manage them can help you stay on track with your treatment.
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Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
Why Mounjaro Causes Gas and Digestive Changes
Mounjaro is a GIP and GLP-1 receptor agonist — it activates two natural hormone pathways that regulate appetite and digestion. One key effect is slowed gastric emptying, meaning food stays in your stomach longer before moving to your intestines. This slower digestion can lead to increased gas production, bloating, and flatulence as your gut bacteria ferment food that would normally move through faster.
Additionally, Mounjaro changes how your body processes fats and carbohydrates, which can alter gas-producing bacteria in your colon. The medication also reduces overall food intake, and when you eat less, the composition of your gut bacteria shifts — sometimes triggering temporary digestive disturbances.
These effects are most common in the first 4–8 weeks as your digestive system adjusts. Many people find symptoms settle significantly after the first month, particularly if they follow dietary guidance. Using our free GLP-1 weight loss calculator, you can track your progress and monitor how your body responds as you move through dose titration.
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
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Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Managing Gas and Digestive Symptoms
Several strategies can help reduce farting and bloating while taking Mounjaro:
- Eat smaller, frequent meals — large meals worsen slowed digestion and gas
- Avoid gas-triggering foods — beans, lentils, cruciferous vegetables (broccoli, cabbage), fizzy drinks, and high-fat foods can increase flatulence
- Stay hydrated — drink water throughout the day to support digestion
- Eat slowly — chewing thoroughly reduces air swallowing and gas
- Ginger tea or peppermint tea — both have been shown to reduce bloating
- Consider over-the-counter remedies — products containing simethicone (like Windsetlers) can help break up gas bubbles
If symptoms persist beyond 8 weeks or become severe, speak to your GP or the prescriber managing your Mounjaro treatment. They can assess whether the symptom is typical or suggests a need for dose adjustment.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Is farting a serious side effect of Mounjaro?
No. Gas and flatulence are common but not serious side effects of Mounjaro. They're caused by slowed digestion and changes in gut bacteria. Most people find symptoms improve significantly within 4–8 weeks as their body adjusts. However, if symptoms are severe or persist beyond 8 weeks, contact your GP or prescriber.
How long does gas last when starting Mounjaro?
Digestive symptoms including gas typically peak during the first 2–4 weeks and improve by week 8. Some people notice improvement within days if they adjust their diet. The timeline varies — individual experiences depend on starting dose, diet changes, and how quickly you adjust doses during titration.
Can I take anything to reduce Mounjaro-related gas?
Yes. Over-the-counter remedies like simethicone (Windsetlers) can help. Peppermint or ginger tea may reduce bloating. Most importantly, eat smaller meals, avoid gas-triggering foods like beans and cruciferous vegetables, and stay hydrated. Eating slowly and chewing thoroughly also helps reduce air swallowing.
Does gas mean Mounjaro isn't working?
No. Gas and digestive changes don't indicate how well Mounjaro is working for weight loss. These are side effects caused by slowed digestion, separate from the medication's appetite-suppressing effects. Track your progress with our free weight loss calculator to see results independently of digestive symptoms.
Should I stop taking Mounjaro if I have gas?
No — discuss with your prescriber before stopping. Gas is a common temporary side effect that usually improves within weeks. However, if symptoms are severe, persistent, or accompanied by severe abdominal pain, contact your GP immediately. Your prescriber can assess whether dose adjustment is needed.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.